After looking at the birth weights of the different generations, the researchers analysed the results of cognitive assessments taken when the study members were 10 or 11 years old.

Across all generations, children born small had much lower cognitive ability than those born at a normal weight. However, the researchers found that the gap had more than halved for children born at the turn of the century than for those born earlier.

The report said: “Low birth weight children born in 2001 would have benefited from a range of medical treatments that were not available to children born in 1958 and 1970. These advancements in medical care helped to prevent brain damage and other negative consequences often associated with low birth weight.”

Surprisingly, more children born in 2000-01 had low or very low birth weights, compared to previous generations. Low birth weight babies were under 2.5kg, and very low birth weight children weighed under 1.5kg.

In every generation, children were more likely to have a low birth weight if they came from disadvantaged families, if their mothers engaged in unhealthy behaviours during pregnancy, and if they were not breastfed. First-born children and girls were more likely to have lower birth weights as well.

The authors noted that “despite medical advancements, a disadvantage associated with low birth weight remains that may be both social and biological, and that appears to be difficult to overcome.”